Great questions! First off, you are welcome to move your brick to whatever works best for your schedule. As we get closer to race day, it would be helpful to have some race specific bricks off of your longer bike effort. Otherwise, you can do them whenever you can fit them in.
As for substituting workouts, this is your choice. But I really do encourage you to try to line up appropriate workouts. For example, if the workout in the training plan calls for drill focused, please line up your OSP drill focused workout. If it calls for tempo or sweet spot intervals, then line up a similar workout. We talked about this at the kick off meeting. This applies to substituting Zwift, TrainerRoad, etc workouts too.
Where the OSP can be very helpful is that it’s providing company for your longer ride efforts that will likely be done on the trainer right now. Thus you can replace the OSP weekend workout for your long ride. However if OSP is only 2 hours. Please recognize that you might need to set up early, stay late or add in a little extra at home to make sure that you are getting in approximate the same amount of time in the saddle that the workout calls for.
Hope this helps!